Basic to understanding the role of specific bacteria in the etiology of periodontal diseases is their accurate recognition and identification. Basic to the identification process is that the strains to be identified must be compared with strains that have been identified (data base). The success of any identification procedure or the evaluation of any (manual or computer automated) identification procedure is dependent upon a data base of accurately identified strains. A major objective of this project is to establish genetic relationships, by DNA homology experiments, among broad groups of bacteria that have been isolated from both normal oral cavities and from those with the various types of periodontal disease. The DNA results will provide the data base on which identification procedures can be evaluated. The second major objective of the proposed study is to investigate the ecology of the oral microbiotota in terms of specific strains. Isolates that are identical can be so identified by DNA homology experiments. We will be able to establish if the flora of the oral cavity of an individual consists of strains that are unique to that individual. If this is so, we will be able to determine if organisms isolated from periodontal disease lesions are part of that individual's normal oral flora and will also be able to determine the effect of chemotherapy upon the resident strains. The third major objective is to determine the distribution of plasmids among strains within the various DNA homology groups. The genetic relationships of these plasmids with each other will be determined by DNA homology. Phenotypic properties will be correlated with the presence of specific plasmids.